P-Delta Effects on Tall RC Buildings with and Without Shear Wall

Transcription

1 P-Delta Effects on Tall RC Buildings with and Without Shear Wall High-rise building is the demand of new era as it provides accommodation to a well number of people in a small place but without proper design and consider catastrophic may Rajat Sharma 1, Raghvendra Singh 2 1M.E. student, UEC Ujjain (MP), 2 Professor, UEC, Ujjain (MP) Dept. of Civil Engineering, UEC, Ujjain, Madhya Pradesh, INDIA *** happen which is evident from last few decades after introduction of high-rise and Reinforced Concrete structures are prone to effected by several parameters for its self-weight and frame system. Abstract - In this modern era of 21st century the urbanization increases worldwide, in heavily populated cities the availability of land is becoming less and cost of land is becoming higher. In view of popularity & less availability of land, tall structures are only solutions for overcoming the problems. A tall structure should be designed to resist the lateral load like Earthquake force within the permissible limits set by Standards. Loads are mainly of two types that are Gravity Loads & Lateral Loads likes Earthquake load. Earthquake forces are further two types, Static Forces & Dynamic Forces. It would be linear and Non-linear also. Linear static analysis can be performed for Low Rise Structure & law earthquake zones only. For tall structure it is necessary to consider nonlinearity, which is generally observed in geometry & materials. Our study is based on P- Delta analysis which incorporates geometric nonlinearity in the analysis. The study will be performed on structural software ETABS. In the present study seismic analysis and wind load analysis of a multi -storey RC building with and without P-Delta effects is analyzed by using ETABS structural analysis software. The seismic zone factor of 0.16 is considered which falls under Zone-III. From the analysis, the displacement respects to earthquake loads are minimum when compared with earthquake load with P-delta effects. P-delta effect is secondary effect on structure.it is also known as Geometric nonlinearity effect. In this study the P-delta effect on high rise building is studied. Linear static analysis (without P-delta effect) on high rise building. For the analysis (20 storey) R.C.C. framed building are modeled. Earthquake load is applied on model of structure as per IS-1893(2002) for zone III in E-Tab software. Load combination for analysis is set as per IS-456(2000). All analysis is carried out in software ETAB. Bending moment, story displacement with shear wall and without shear wall and p-delta effect is calculated. The P- Delta effects found to decreases the storey displacement by earthquake using shear walls and also decrease by wind loading. Axial force increases as no. of building storey increases. Bending moment is increases in column at ground floor found 9% increases and also in shear walls 5.96 % increases after P-delta effects. Key Words: P-Delta effect, displacement, bending moment, lateral loads, liner static, shear walls, tall buildings. 1. INTRODUCTION Generally, the analysis of buildings is done by using linear elastic methods, which is first order structural analysis. In a first order analysis displacements and internal force are evaluated in relation to the geometric un deformed structure. However, in some cases, the deflection of the structure can have a geometric second order effect on the behavior of the structure. This type of geometric nonlinearity can be analyzed by performing through iterative processes which is only practicable by using computer programs. It is generally known as second order analysis. In this type of analysis, the deformations and internal forces are not proportional to the applied loads. Second-order effects are generally explained by considering the additional displacements, forces, and moments which generated from the use of actions on a deflecting structure. These are known as second-order effects. In certain situations, a first-order analysis may be used to estimate the effects of a second-order analysis by procedure, which is suitable for elastic frame analysis by computer. Second order effects introduce additional deflections, moments and forces beyond those calculated by first-order analysis. So it should be considered in the design. 1.1 P-DELTA EFFECT P-Delta is a non-linear (second order) effect that occurs in every structure where elements are subject to axial load. It is a genuine effect that is associated with the magnitude of the applied axial load (P). Due to which, the structure is pushed even further developing a second order deflection. This second order effect experienced is conveniently termed as P-Delta effect. If P is the gravity load, Δ1 is the displacement observed through first order or elastic analysis for lateral forces (Fwind or Feq) and h is the story height, the product (P Δ1) is the overturning moment experienced in addition to F h. The P-Delta effect is illustrated in the Figure 1, where the Δ2 is the second order deflection developed due to P-delta effect. This secondary effect is observed by two different processes. The major effect is seen due to deflection of the structure as a whole (frame instability) and also termed as P - BIG delta (P-Δ) and the rest is contributed by the axial deformations of individual members of the structure (member instability), 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1992

2 also termed as P - little delta (P-δ) (Chen and Wang 1999; Dobson 2002). However, this thesis research is only limited to the P-delta effect seen through structural instability (P- Δ). The magnitude of P-Delta effects depends on the magnitude of axial load (P), Stiffness / slenderness of individual elements and structure as a whole (Dobson 2002). So, normally tall structures and buildings with higher number of stories will experience higher P-delta effect than others and have to be designed with adequate considerations to it. The importance of P-Delta non-linear analysis is continuously increasing as new generation high rise buildings are getting more and more popular. Beam Size Slab Thickness External Wall Shear Wall Zone Region Live Load Floor Finish Load Earthquake Load Wind Load Response Reduction Factor 300mmx500mm 150mm 200mm 150mm III Indore 3KN/sqm 1KN/sqm As Per IS:1893(Part-I)-2002 As Per IS:875:1987(Part-3) 3.0 Zone Factor 0.16 Seismic Intensity Wind Speed Moderate 39m/s Terrain Category 1.0 Structure Class A Fig.1: P-Delta Effects on a Cantilever Column 2. MODEL CONFIGURATION The general layout of the building is shown in Figure-2. Preliminary sizes of structural components are assumed by experience and general information of building as shown in Table-1.In this direction, four identical shear walls are located along four side of the building. The shear walls are assumed to be fixed at their bases. The 3D view of building as shown in Fig.3a & b. Fig.2: Plan of Building Table-1 Details for Building Models Details for Building Models Particular Plan Size Details 70.00mx13.50m No. of Floors Storey Height m Type of soil 1.0 Grade of Concrete Grade of Steel Column Size M25 and M30 Fe415 (Rebar) 500mmx500mm and 300mmx500mm Fig.3 (a) 3D view without shear wall 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1993

3 1. Zone factor, Z = 0.16 (Zone III) 2. Importance factor I = Response Reduction factor, R =3 4. Soil type = Hard Soil 5. Damping Coefficient = RESULTS AND DISCUSSIONS he results of the P-delta, displacement due to earthquake and wind load with and without shear wall calculations for each model are presented. 4.1 Displacement Fig.3 (b) 3D view with shear wall 3. LOAD CALULATION 3.1 Gravity Load The loads considered for the following study are as below which are according to IS codes. 1. Dead load: The self-weight of the structural members is calculate according to the code provisions and is taken care in the software. 2. Live load on floor: 3kN/m 2 (Table 1 of IS 875(Part- 2):1987) 3.2 Wind Load Wind load calculations as per Indian code: IS 875 (Part- 3)1987) Design wind speed (V z) can be mathematically expressed as follows Vz = V b K 1 K 2 K 3 Where, V b = basic design wind speed K 1, K 2, K 3 can be calculated from the IS: 875 (part3) P z = Design wind pressure 3.3 Earthquake Load P z = 0.6 Vz 2 As per IS , seismic analysis of the structure is performed. The design horizontal seismic coefficient, Ah for the structure has been computed using the following: For the earth quake load storey displacement with P-delta effects along the height of the building is shown in Fig.3a,b. The storey height is plotted in X-axis and Storey displacement is plotted in Y-axis. Displacement of without shear wall model is seen as shown in Table-2 Storey Table-2: Displacement due to earthquake (without shear wall) Without p-delta With p-delta X-dir Y-dir X-dir Y-dir Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1994

4 Fig.3 (A) Displacement due to Earthquake without shear wall & without P-Delta Storey Storey Storey Storey Storey Storey Storey Fig.3 (B) Displacement due to Earthquake without shear wall & with P-Delta Fig.4 (A) Displacement due to Earthquake with shear wall & without P-Delta For the earth quake load storey displacement with P-delta effects along the height of the building is shown in Fig.4a,b. The storey height is plotted in X-axis and Storey displacement is plotted in Y-axis. Displacement of with shear wall model is seen as shown in Table-3 Table-3: Displacement due to earthquake (with shear wall) Storey Without p-delta With p-delta x-dir y-dir x-dir y-dir Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Fig.4 (B) Displacement due to Earthquake with shear wall & with P-Delta For the wind load storey displacement with P-delta effects along the height of the building is shown in Fig.5a,b. The storey height is plotted in X-axis and Storey displacement is plotted in Y-axis. Displacement of without shear wall model is seen as shown in Table-4 storey Table-4: Displacement due to wind load (without shear wall) without p-delta with p-delta x-dir y-dir x-dir y-dir Storey Storey Storey , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1995

5 Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Fig.5 (A) Displacement due to wind load without shear wall & without P-Delta For the wind load storey displacement with P-delta effects along the height of the building is shown in Fig.6a,b. The storey height is plotted in X-axis and Storey displacement is plotted in Y-axis. Displacement of with shear wall model is seen as shown in Table-5. Table-5: Displacement due to wind load (with shear wall) Storey Without p-delta With p-delta x-dir y-dir x-dir y-dir Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Storey Fig.5 (B) Displacement due to wind load without shear wall & with P-Delta Fig.6 (A) Displacement due to wind load with shear wall & without P-Delta 2017, IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1996

6 Fig.6 (B) Displacement due to wind load with shear wall & with P-Delta Along the height of the building auto lateral load for the Earth quake load is shown in fig-7. Storey height is plotted in X-axis and lateral force is plotted in Y-axis. For Earthquake load case the value of axial force are tabulated in table 6. Maximum axial force is seen in the Storey 20 and minimum lateral force is seen at Base. Table-6: Auto lateral load for earthquake Storey Elevation (m) Lateral Load (KN) Story Story Story Story Fig-7: Auto lateral load verses storey height due to Earthquake load in general The results for Bending Moment values of column C18 are described below in Table-7 and Fig.8. S. N Table-7: Bending Moment at Base of column C18 Load Case Without P-Delta With P- Delta % Difference 1 1.2(DL+LL+EXQ) (DL+LL-EXQ) (DL+LL+EQY) (DL+LL-EQY) DL+1.5LL+1.5WLX DL+1.5LL+1.5WLY Story Story Story Story Story Story Story Story Story Story Story Story Story Story Story Story Base 0 0 Fig-8: P-Delta Effect for C18 The results for Bending Moment values of shear wall P1 are described below in Table-8 and Fig-9. In this Table six load cases are described with P-Delta and Without P-Delta and also shown percentage difference. SN Table-8: Bending moment at base of shear wall p1 Load Case Without P- Delta With P- Delta % Differenc e 1 1.2(DL+LL+EXQ) (DL+LL-EXQ) (DL+LL+EQY) , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1997

7 4 1.2(DL+LL-EQY) DL+1.5LL+1.5WLX DL+1.5LL+1.5WLY Atmanand Saraswati Institute of Technology, Surat, Gujrat, India. 2. Dhavde, Rao, Rupanvar, and K. (2015), Assessment of P-Delat Effect on High Rise Buildings S.B. PATIL Collage of Engg, Indrapur, pune, India. 3. Rizwan Akhter (2017), P-Delta Effect on High Rise Building Subjected to Earth Quake and Wind Load Al- Falah Univercity, Faridabad, India. 4. Dinar, Karim, and Barua (2013). P-Delta Effect in Reinforced Concrete Structures of Rigid Joint, University of Asia Pacific, Bangladesh. CONCLUSIONS Fig-9: P-Delta Effect for Shear Wall P1 This chapter presents the major conclusions and future scope of the p-delta effects on Tall RC building with and without shear wall. 1. The P-Delta effects found to decreases the storey displacement by earthquake using shear walls and also decrease by wind loading. 2. The result obtained that axial force increases as no. of building storey increases. 3. Bending moment in column at ground floor found 9% increases after the P-delta analysis. 4. The results show the bending moment in shear walls 5.96 %increases after P-delta effects. 5. Displacements with respect to earthquake load with P- delta effects are higher when compared with earthquake load. 6. Storey displacement values for all the load cases are within the permissible limit. 7. This concludes P-delta effects have more effect in designing of a structure rather than linear order effects. 8. As number of storey increases P-delta effect becomes more important when shear wall provided. 9. It is necessary to check the results of analysis with and without considering P-delta effect for the buildings. 10. So, we should perform P-delta analysis for designing a 20 storey building with and without shear walls. 11. The conclusion is valid for RCC residential buildings for wind loading and seismic loading in all the zones of India. REFERENCES 1. Mangukiya, Ravani and Miyani (2017). Study of P- Delat Analysis for R.C. Structure, Shree Swami 5. Mollick (1997), Experimental Study on P-Delat Effect in RC High Rise Building, The Institute of Engineers, Bangladesh 6. Lakshmi Subash (2017). Influence of P-Delta Effect on Reinforced Concrete Buildings with vertical Irregularity-A review, Sreepathy Institute of Management And Technology,Vavanoor,Kerala,India. 7. Shah Mrugesh D., Desai Atul N (2011), Performance based on analysis of R.C.C. frames, National Conference on recent Trends in Engineering and technology,. V.M. engineering college, V.V Nagar, Gujarat, India. 8. Agarwal.P. and Shrikhande. M,(2006) Earthquake Resistant Design of Structures Prentice-Hall of India Private Limited, New Delhi, India. 9. Mallikarjuna B.N, Ranjith A(2014), Stability analysis of steel frame structures: p-delta analysis, IJRET, Vol.03 Issue: 08,Aug-2014, pp Rafael Shehu(2014), The p-δ-ductility effect : overview the effect of the second order in the ductile structures European Scientific Journal, Vol.3,2014, pp Regina Gaiotti1 and Bryan Stafford Smith2 (1989) P- Delta Analysis of Building Structures. Published in Journal of Structural Engineering vol. 115, ASCE, India. 12. IS- 1893(Part I) 2002 Criteria for Earthquake Resistant Design of Structures. 13. Moghadam A.S., Aziminejad A., (2004), Interaction of Torsion and P-Delta Effects in Tall Buildings, Proceedings, 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada., Paper No , IRJET Impact Factor value: ISO 9001:2008 Certified Journal Page 1998